[M]y guess is that suffering is an evolved elaboration on pain unique to social mammals or possibly shared by social organisms of all sorts. It seems likely to me to basically mediate an exchange of long-term status for help from group members now.People often complain that it is difficult to construct an algorithm that can choose which animals we should favor and which we should not, given our limited resources (for example, see Jonah Lehrer here). Too often we rely on the cuteness factor. If correct, Vassar's theory has clear policy implications if we want to reduce animal suffering: save the social animals.
This essay argues persuasively that the most utilitarian suffering to curb is not that felt by animals in captivity, nor by other humans, but instead by animals that live in nature.